/// 设置元素的float属性
/// @param  {[string]} $direction      [left] float方向
/// @param  {[boolen]} $support-for-ie [true] 是否支持IE
/// @link https://gist.github.com/airen/d7f8ad25c982750dcb86
@mixin float($direction: left, $support-for-ie:true) {
    float: unquote($direction);
    @if $support-for-ie {
        _display: inline;
    }
}